Italy’s bigger cities, especially Rome, have plenty of churches to please those with morbid fascinations for skulls, skeletons, and saintly relics. Taken together, these churches and their contents provide a sort-of museum feel — creepy but not altogether isolating.

Over the weekend, I finally got the chance to check out Milan’s famed Duomo, that jagged, Gothic behemoth that defines the city’s traditional skyline. Also known as Santa Maria Nascente (Saint Mary of the Nativity), the Duomo is the second largest…